The primary objectives of our research project are: 1) to elucidate the mechanism by which cholesterol synthesis in brain is regulated during and after development, and 2) to determine the role of cholesterol esters and cholesterol ester metabolizing enzymes in the processes of myelination and demyelination. In a recent study we have demonstrated that soluble fraction from brain contains specific binding sites (proteins) for lanosterol (methyl sterols), desmosterol and cholesterol, and delta 7-dehydrocholesterol. We plan to isolate these proteins from brain S105 by gel filtration techniques, and further establish the ligand binding specificity. We will determine the role of these specific proteins from brain S105 in the conversion of various sterol precursors to cholesterol by microsomes from brain. In order to identify the enzymatic reactions that show age dependent alterations and thereby become rate limiting for cholesterol synthesis in brain, we have investigated in our earlier studies the activities of mevalonate kinase, phosphomevalonate kinase and pyrophosphomevalonate decarboxylase in brain S105 at various stages of development. We reported that decarboxylation of pyrophosphomevalonate in brain may be one regulatory step in cholesterol synthesis. We plan to assay brain S105 at various stages of development for the activities of the following enzymes: HMG CoA synthase, HMG CoA lyase, isopentenyl pyrophosphate isomerase, dimethylallyl transferase and pyrophosphatase(s) which hydrolyze isopentenyl pyrophosphate, dimethylallyl pyrophosphate and farnesyl pyrophosphate. Another aim of this project is to study the role of cholesterol esters and cholesterol ester metabolizing enzymes in the processes of myelination and demyelination. To attain this objective we plan to investigate, whether in experimental demyelination increase in concentrations of cholesterol esters in brain is associated with reduced activity of cholesterol ester hydrolase.